Maybe you can guess what the app does.

Does it tell your coworkers when they need more deodorant?

 

Weather reporters are caught in the same pattern as news reporters. They are making every attempt to increase the perceived importance of what they have to say. This includes a myriad of confusing graphics, sound effects, and terminology to add drama to the presentation. It's another "sign of the times" in which we live: the age of short attention spans.

 

I haven't followed this thread much because 980 posts about the weather seemed ... excessive.

The alternative is 10,000 posts about how to connect an LED to mains.

 

No, the lower the dew point, the dryer the air and the greater the imbalance between liquid water (Sweat) and vapor.

To ventilate holds loaded with cargo that could be damaged by moisture you always compare the inside DP with the air DP. As long as air has a lower DP, you ventilate. Exactly the same reasoning they used in the old times, to ventilate or not the "santabarbaras", (powder-magazines) in old warships.

Wet and dry bulbs readings entered regularly in the log book, were compulsory in the old times for certain vessels. They formed part of the information sent every 12 hours to shore stations collecting meteorological information.

 

Pretty neat. Do they have an app. that can monitor and display DP?

 

To ventilate holds loaded with cargo that could be damaged by moisture you always compare the inside DP with the air DP. As long as air has a lower DP, you ventilate. Exactly the same reasoning they used in the old times, to ventilate or not the "santabarbaras", (powder-magazines) in old warships.

Wet and dry bulbs readings entered regularly in the log book, were compulsory in the old times for certain vessels. They formed part of the information sent every 12 hours to shore stations collecting meteorological information.

Fascinating. That's getting very close to what my app does.

 

Pretty neat. Do they have an app. that can monitor and display DP?

Any weather app can give you DP, relative humidity and wet bulb. All give an idea of the same thing, the wetness of the air. Energy content (enthalpy) is nearly proportional to wet bulb. Humidity – not relative, but the amount of water per unit of dry air – is proportional to dew point.

 

Wow, now I realize that my question wasn't that stupid after all. Things sure are a bit more complicated than they seem when you take a closer look at them.

Wayneh, I'm guessing that your app simplifies the interpretation of DP relative to other parameters to help you decide a course of action on whatever it is that the user is managing.

#12, when I started reading your post I thought that you were pulling my leg... Psycho... what? But then I read more closely and saw PsychRo-something instead. Fascinating chart... will study it, and probably get back to you with a million more questions. Thanks!

Also, thanks for the link, Joe. It sure looks like a very informative tool.

 

Fascinating. That's getting very close to what my app does.

Not sure what they use nowadays in very specific vessels. Something like your app surely would be appreciated.

Reefer vessels also control (and manage) much more parameters including CO2 content. That is delicate cargo. Ask anyone in the business how demanding are eggs or bananas as cargo.

For bulk carriers, it is important the cargo humidity content at loadport and sea temperatures during voyage. There is a dreaded thing called "ships sweating" competing with "cargo sweating".

Many cereal byproducts must stay in storage prior loading to allow a certaing cool down. Linseed pellets if loaded too warm, could end being a hard block of cargo that no grab or vacuvator could discharge. Been there...

Google for coal or fish meal even corn and the possibility of fire on board. Not a nice thing. Been there too.

Steel coils in closed packaging loaded with high humidity content in a warm country - Brazil as an example, could give nasty surprises at the dischport.

I was Ch. Off in a vessel where, no matter what we did to ventilate cargo in hold No. 3 as per the rules, when opening covers at destination, the cargo exhibited a glorious thick layer of dew atop the bulk.

And the, reefer containers came....

 

Wow, now I realize that my question wasn't that stupid after all. Things sure are a bit more complicated than they seem when you take a closer look at them.

That's one of the first things you learn in college...no matter which subject you choose, there are people that are decades ahead of you.
Another way to put it is, The more I learn, the more I realize how much I don't know.
Add to that the plasticity of the human brain and you realize that no matter how good you get, a couple of years of disuse and people who stayed in that kind of work are ahead of you just because you forgot some of what you used to know.

One of my primary purposes in being at AAC is to keep the rust off my electronics brain cells.

Fascinating chart... will study it, and probably get back to you with a million more questions. Thanks!

That chart took up a week of class time just to get familiar with it. Obviously more time to get good at it.

 

That chart took up a week of class time just to get familiar with it. Obviously more time to get good at it.

How often do you use it?

 

How often do you use it?

Not much. I used it for wayneh in his humidifier quest. I use it for original A/C designs or strange stuff like a printing shop where humidity control is as important as temperature control. It's pretty useless for day to day A/C repairs and replacements unless you get into a question like tcmtech, "Why doesn't a new A/C work as well as a 30 year old A/C?" That's when I get down to the nitty gritty on measurements.

 

"Why doesn't a new A/C work as well as a 30 year old A/C?"

Well... why doesn't it?

Don't bother writing a long reply if you've already answered that question. Posting a link to your previous answer (or to an article that you think adequate and informative) would suffice, at least for me.

 

Well... why doesn't it?

Look at wayneh's humidifier Thread.

 

I just scrapped two DE-humidifiers this morning, one about 20 or more years old and the other is the newer one that replaced it about 6 years ago. The older one weighs 3 times as much, and a lot of that is the compressor, which is probably 3 fold larger in terms of volume. The heat exchanger coils are easily twice as large, maybe 3 times.

The fan and air flow of the old unit was puny compared to newer units, which use centrifugal squirrel cage fans instead of the old 4-blade axial fan. Of course the newer units have electronic controls and LED indicators and such, versus the old-fashioned mechanical controls on the old unit.

My new A/C will be here tomorrow!

 

My new A/C will be here tomorrow!

Are you going to use it as a dehumidifier?

 

Wayneh, I'm guessing that your app simplifies the interpretation of DP relative to other parameters to help you decide a course of action on whatever it is that the user is managing.

Close. It uses psychrometric data about inside air and compares it to outside air (with data from checking the local weather), and produces a decision on whether to prefer outside air for ventilation. Should I open the windows, or not?

It does a few other things but I don't want to spill everything until it's in the app store.

I developed it in part because my wife often drives me crazy by opening the window "because it's only 68°F out!" when the dew point is also 68°F, which is miserable to me. I'd much rather sleep in dry air at 72° than pea soup at 68°. Maybe she'll listen to the app.

 

Are you going to use it as a dehumidifier?

Yes! I'll set it on a stand in the basement, and find a way to route the water out of the machine and into the floor drain.

 

That chart took up a week of class time just to get familiar with it. Obviously more time to get good at it.

Yup, I can remember struggling with it a lot the first time through, and any time I haven't used one for a while. Don't get me started on Mollier diagrams!

One thing that helped me grasp the psychrometric chart is the realization that two vital physical concepts are brought together in one chart: The vapor pressure of water as a function of temperature (which explains the characteristic curve of the chart), and the Ideal Gas Law. Moist air is just a blend of two ideal gases. You can reproduce the chart yourself (as my app does) by applying little more than those two concepts. If you need great precision, there are kludges to adjust for non-ideality but those are optional add-ons.

If you're really into such things, there is a bizarre property of water that makes the chart much simpler than it might be. For water, and ONLY water, the iso-wet bulb lines are also iso-enthalpy lines. If you know the WB, you know the enthalpy. Stunning coincidence.

Woohoo! The 1000th post!

 

Woohoo! The 1000th post!

Oh you, ... odometric snob